Vulcanized rubber containing bis-3, 4-dimethyl-6-alkylphenol monosulfides and process of making same



2,822,414 Patented Feb. 4, 1958 VULCANIZED RUBBER CONTAINING BIS-3,4-DI-NIETHYL 6 ALKYLPHENOL MONOSULFIDES AND PROCESS OF MAKING SAME Harry E.Albert, Akron, Ohio, and Lloyd 0. Bentz, Lancaster, Pa., assignors toThe Firestone Tire & Rubber Company, Akron, Ohio, a corporation of OhioNo Drawing. Application December 24, 1953 Serial No. 400,345

6 Claims. (Cl. 260-810) This invention relates to antiozone agents whichinhibit is in a methyl, ethyl or propyl group, as well as cycloalkylgroups of seven, eight or nine carbon atoms. The agents of thisinvention will be more particularly illustrated in what follows.

Oxygen and ozone both have a harmful eflect on rubber, but the effect ofeach is different, and compounds which inhibit or prevent the harmfulefiect of one are not necessarily effective in stopping the harmfuleffect of the other.

Crabtree and Kemp in an article in Industrial and Engineering Chemistry,vol. 38, starting at page 278 (1946) explain the difierence in theaction of oxygen and ozone. The light-catalyzed oxidation which occursduring outdoor exposure forms a skin and crazed appearance over theexposed surface of the rubber. Ozone, even in very low concentration,attacks stretched rubber only (C. H. Leigh-Dugmore, Rubber Age andsynthetics, November and December 1952) and forms cracks perpendicularto the direction of stretch, and such cracking can occur in the absenceof light.

As a matter of fact, practically all commercial rubber antioxidants arewithout eifect in inhibiting the deterioratron caused by ozone. Theinhibitors of this invention do not absorb or act directly on the ozone,but have some unknown action in preventing the cracking which isassociated with ozone exposure in stretched natural rubber.

Natural rubber is used in the manufacture of the whitesidewalls oftires. The cracking of such sidewalls has long been a problem. It isoften very extensive, and because of the color of the sidewall it isvery noticeable. it is a primary object of this invention to provideantiozone agents which prevent such cracking without discoloring thesidewall. However, the antiozone agents of this invention are notlimited to that use but can be employed in black sidewalls, treads,thread and other latex products, and other rubber products.

Tires are stressed when inflated. While a tire is at rest it isstretched statically, and on a moving vehicle it is stretcheddynamically. Some of the antiozone agents are more etfective in statictests and others are more effective in dynamic tests. Antiozone agentseffective under both conditions will be desired for tires, but for otherrubber products an antiozone agent which does not meet both tests can beused. The inhibitors "of this invention include, for example:

Bis-3,4-dimethyl-b-isopropylphenol monosulfideBis-3,4-dimethyl-6-t-butylphen01 monosulfideBis-3,4-dimethyl-6-sec.-butylphenol monos ulfide Bis-3,4-dimethyl-6-sec.-amylphenol mono'sulfide Bis-3,4-dimethyl-6-t-arnylphenolmonosulfide Bis-3,4-dimethyl 6-n-hexylphenol monosulfideBis-3,4-dirnethyl-6-tt-octylphenol monosulfideBis-'3,4-dimethyl-6-nonylphenol mono'sulfideBis-3,4-dimethyl-6-cyclbhexylphenol monosulfideBis-3,4-dimethyl-6-cyclopentylphenol monosulfideBis-3,4-dimethyl-6-a-methylbenzylphenol monosulfide The inhibitingeffect of the antiozone agents in rubber was determined by treatment ofunaged, cured stocks with air of controlled low ozone content inspecially designed equipment and also by outdoor exposure to naturalweathering. The tests were conducted with one-half inch dumbbell samplesof approximately 100 gauge thickness; The special apparatus for testingwith air of controlled low ozone content and the method of testingtherein are described in the articles by Ford and Cooper, appearing inIndia Rubber World for September and October 1951, entitled A study ofthe factors affecting the weathering of rubber-like materials-l and II.The following reports of such tests give the ozone concentrationmaintained during each test in parts per 100,000,000 parts of air, theduration of the test, and the temperature used. Two types of tests wereconducted. In one type-called the dynamic testthe sample was repeatedlystretched between the limits of 0 and 20 percent elongation 'at the rateof 108 cycles per minute. In the other type of test the static testthesamples were stretched at 12.5 percent elongation throughout the test.No special lights were used in either test. On completion of each testthe size of the cracks in each sample was compared visually With thesize of the cracks in a blank which contained no antiozone agent andwhich was curred and tested at the same time as the test sample. Thesize was determined according to an arbitrary scale of measuring, usingthe numerals O, 1, 2, 3, 4 and 5 to represent no visual cracking andcracks which were very fine, fine, medium, coarse and very coarse,respectively.

The reported results include data on the tensile prop erties of thecured rubber stocks before and after aging 2 days in an oven at 212 F.The modulus and tensile strength are given in pounds per square inch andthe elongation is reported as percent of stretch at the break. Thesedata are included to show that the antiozone agents have no substantialdeleterious effect on the cure or upon the aging of the cured stocks.

The antiozone agents were tested in white stock such as might be used inwhite sidewalls for tires, and also in stock such as that which might beused in tire treads. The blanks of the white stock were compoundedaccording to the following formula:

Parts by weight Natural rubber 100 White pigment and filler 90.2 Stearicacid 1.2 Sulfur 3.0 Accelerator 0.9

All blanks and test samples of white stock were cured minutes at 280 F.

The blanks used for testing the effect of the anti-ozone 3 agents intread stock were compounded according to the following formula:

Parts by weight All blanks and test samples of tread stock were cured 45minutes at 280 F.

In all of the test samples, both those tested in the special apparatusand those subjected to natural outdoor weathering, 2.0 parts by weightof the antiozone agent was added to the blank formula for each 100 partsby weight of the rubber present. Any relatively small amount can beemployed, and this can vary, for example, from 0.2 part by weight toparts by weight, depending upon the use to be made of the rubbercomposition.

The following examples illustrate the invention.

The first table illustrates the use of two different agents in whitestock. Table 2 illustrates the use of one of these agents in the whitestock and Table 3 records the results of tests run at different times,with the other agent in a white stock. Table 4 refers to the results ofa test in tread stock. All of the foregoing give tensile propertiesbefore and after aging, as well as the results of ozone tests conductedin the special apparatus. Tables 5, 6 and 7 give the results of exposingdifferent samples of White stock containing ditferent antiozone agentsto natural weathering for different periods of time. Table 8 records theresults of a similar test on tread stock.

Table 1.-White stock Blank 195. 3 195. 3 195. 3BigfiA-dimethyl-G-sec.-butylpl1enol monosule 2Bis3,4-dimethyl-fi-t-butylphenol monosulfide. 2 Normal TensileProperties:

400% Modulus 900 825 800 Tensile Strength... 3, 525 3, 290 3, 300

Elongation at Break 680 635 635 Aged 2 Days in Oven at 212 F.:

400% Modulus 750 800 675 Tensile Strength... 1, 325 1, 750 1, 750

Elongation at Break 470 525 550 OzEone Effects (7 Hrs. at 60 p. p. h. m.and 95 Static 4 0+ 0+ Dynamic 4- 0+ 0+ Table 2.-Whzte stock Blank 195. 3195. 3 Bis-SA-dimethyl-G-sec.-buty1phenol mnnosulfide 2 Normal TensileProperties:

0% 0d us.-- 900 925 Tensile Strength. 3, 550 3, 525 Elongation at Break.625 615 Aged 2 Days in Oven at 400% Mod 850 850 Tensile Strength 2, 0252, 150

Elongation at Br 550 555 Ozone Efiects (7 Hrs. at 60 h. m. and 95 F.):

Static 4+ 1 Dynamic 4+ 1 1- Table 3 .-White stock Blank 195. 3 195. 3195. 3 195. 3 Bis 3,4 dimethyl -6- tbutylphenol monosulfide 2 2 NormalTensile Properties:

460% lviodulus l, 025 l, 025 925 800 Tensile Strengtln. 3, 450 3, 275 3,675 3, 480

Elongation at Brea Aged 2 Days in Oven at l i l I 4 Table 4.-Tread stockBlank Bis-3,4-dlmethyl-6-sec.-butylphenol monosulflde..

Normal Tensile Properties- 400% Modulus- Elongation at Bre Aged 2 Daysin Oven at 212 F Modulus Tensile Strength- Elongation at Break 300 OzoneEffects (14 Hrs. at 25 p. p. h. m. and room temperature):

Static 3+ 0+ Dynamic 3+ 0 Table 5 .Evaluation of natural weathering onwhite stock after Outdoor exposure Table 6.Eval1mti0n of white stockafter outdoor Table 7.Evaluati0n of white stock after outdoor exposureAfter 30 Days Front Back Edge sec.-butylphenol monosuli'ide 2 Table8.Evaluation of tread stock after outdoor Each of the foregoing tablesshows that the test samples containing an antiozone developed muchsmaller cracks than the blanks containing no antiozone agent.

The recorded results are illustrative. The antiozone agents can be usedin rubber compositions compounded for use in tires and for latexcompositions compounded for use in rubber thread and in other rubberstocks.

By sulfur vulcanization is meant the curing of rubber by reaction witheither free sulfur or a vulcanizing agent of the sulfur-donor type.Known agents of the latter type include the various phenol polysulfidesincluding the alkyl derivatives thereof, the xanthogen polysulfides, thethiuram disulfides and polysulfides, various amine sulfides includingdialkylamine polysulfides and reaction products of primary amines withexcess sulfur. Known vulcanization accelerators are useful in speedingup the vulcanization process and are operative herein, especially therelatively active accelerators including the thiazole sulfenamides, e.g. N-cyclohexyl-2-benzothiazolesulfenamide, thiazoline sulfenamides,thiocarbamyl sulfenamides, mercaptothiazoles, mercaptothiazolines,thiazolyl monoand di-sulfides, the N,N-dialkyl-dithiocarbamates,

the thiurarn sulfides, the xanthogen sulfides, metallic salts ofmercaptothiazoles or mercaptothiazolines or dithiocarbamic acids. One ormore accelerator activator is often used with any of the acceleratorsmentioned, and such activators include the various derivatives ofguanidine known in the rubber art, amine salts of inorganic and organicacids, various amines themselves, alkaline salts such as sodium acetateand the like, as well as other activators known to the art.Additionally, two or more accelerators or accelerator combinations aresometimes desirable in a single rubber compound. Many of theaccelerators mentioned above are suitable in latex formulations,especially such common accelerators as piperidinium pentamethylenedithiocarbamate, zinc butylxanthate, zinc ethylxanthate, zinc salt ofmercaptobenzothiazole, zinc dimethyldithiocarbamate, and zincdibutyldithiocarbamate. Although vulcanization is usually accomplishedby heating a vulcanizable rubber composition at a temperature in therange of 240 to 400 F. for a time ranging from several hours to a fewseconds, vulcanization does take place at lower temperatures such asordinary room temperature. It is quite common to vulcanize a latex filmcontaining an ultra accelerator by allowing the film to remain at roomtemperature for several hours or a few days.

What we claim is:

1. A sulfur-vulcanized composition of natural rubber which contains asmall amount of a bis-3,4-dimethyl-6-substituted-phenol monosulfide inwhich the G-substituent is a hydrocarbon radical of not less than threecarbon atoms and not more than nine carbon atoms and includes analiphatic carbon that is joined to the phenol.

2. A sulfur-vulcanized composition of natural rubber which contains asmall amount of a bis-3,4-dimethyl-6- alkylphenol monosulfide in whichthe alkyl group contains three to nine carbon atoms.

3. A sulfur-vulcanized composition of natural rubber which contains asmall amount of a bis-3,4-dimethyl-6- butylphenol monosulfide.

4. The process of sulfur-vulcanizing a composition of natural rubberwhich comprises vulcanizing such composition in the presence of abis-3,4-dimethyl-6-substituted-phenol monosulfide in which the6-substituent is a hydrocarbon radical of not less than three carbonatoms and not more than nine carbon atoms and includes an aliphaticcarbon that is joined to the phenol.

5. The process of sulfur-vulcanizing a composition of natural rubberwhich comprises vulcanizing such composition in the presence of abis-3,4-dimethyl-6-alkylphenol monosulfide in which the alkyl groupcontains three to nine carbon atoms.

6. The process of sulfur-vulcanizing a composition of natural rubberwhich comprises vulcanizing such composition in the presence of abis-3,4-dimethyl-6-butylpheno1 monosulfide.

References Cited in the file of this patent UNITED STATES PATENTS2,364,338 Beaver Dec. 5, 1944 2,581,919 Albert Jan. 8, 1952 2,581,930Albert Jan. 8, 1952 2,700,691 Mayes Jan. 25, 1955 2,731,443 Forman Jan.17, 1956

1. A SULFUR-VULCANIZED COMPOSITION OF NATURAL RUBBER WHICH CONTAINS ASMALL AMOUNT OF A BIS-3,4-DIMETHYL-6-SUBSTITUTED-PHENOL MONOSULFIDE INWHICH THE 6-SUBSTITUENT IS A HYDROCARBON RADICAL OF NOT LESS THAN THREECARBON ATOMS AND NOT MORE THAN NINE CARBON ATOMS AND INCLUDES ANALIPHATIC CARBON THAT IS JOINED TO THE PHENOL.